Definición de loose cannon en inglés:

sustantivo

The establishment feared him as passionate and unpredictable - a loose cannon.

She'd changed quite a bit since the days of her being classified as a loose cannon and an unpredictable quality on the field.

Then there is the loose cannon of the Juventus side, the unpredictable genius who gives them an ability to score from nothing, a player capable of becoming the best in the world, if only he can curb his dark side.